External rotors for the contactless transmission of rotary movements can be designed for example as couplings, the function of which is based on the effect of a magnetic field; in drive technology, these are called magnetic field couplings. Such magnetic field couplings are employed according to the prior art in order to contactlessly transmit rotational moments across an air gap or through a wall and are therefore often employed in fluid-flow machines such as for example fluid pumps.
From EP 1 239 572 A2 a generic external rotor for the contactless transmission of rotary movements, specifically a magnetic coupling, is known, which comprises two magnetic coupling elements, which are mechanically decoupled from one another through a gap. The two magnetic coupling elements are magnets which are polarised in a segmented manner, which are each attached on the face ends facing one another.
In order to be able to achieve as high as possible an efficiency of such an external rotor it is already known to design permanent magnets of an external rotor in an annular segment form and to arrange these alternatingly in a closed ring in circumferential direction. Because of this it is possible to utilise the complete space that is available in order to place individual permanent magnet segments there. Because of this, a closed annular arch of individual permanent magnet segments can thus be formed. In certain applications it is additionally desirable that the individual permanent magnet segments of the external rotor are embedded into a pocket of the external rotor, which prevents axial shifting or detaching of the permanent magnet segments. Inserting known annular segment-shaped permanent magnet segments in such a pocket of the external rotor however is exclusively possible by axially inserting at least the “keystone”, since closed annular arches cannot be otherwise constructed from the individual permanent magnet segments. Alternatively to this, arranging the individual permanent magnet segments in the external rotor is merely possible in a form that is not completely annularly closed.